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The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2 x 10(-6) m(3) kg(-1) and its Néel relaxation time at about 10(-10) s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30 microT at 1 MHz, as measured via Raman spectroscopy. After 2 h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale.

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NbN films on sapphire or copper substrates have been prepared by magnetron sputtering in argon-nitrogen atmospheres. The highest transition temperature, T c=15.7 K, was achieved with a film sputtered on a sapphire substrate at a substrate temperature T s=800°C and a partial nitrogen pressure P N2 =5×10-3 Torr. Uniform films with transition width narrower than 0.4 K were prepared with good reproducibility by this method. A short NbN tape of metallic luster stripped off from the copper substrate still showed a T c of ∼15 K even after being bent to a radius of curvature as small as 6 mm. These results indicate that magnetron sputtering is useful for preparing NbN films and long NbN tapes.

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